1. Technical Field
The present invention relates to a gyro sensor module for detecting an angular velocity to know an azimuth and an angular velocity detection method.
2. Related Art
A gyro sensor is used in a navigation system mounted in a vehicle or the like. The angular velocity to be detected by the gyro sensor when the vehicle makes a turn is used to know the azimuth of the vehicle. In order to detect the angular velocity accurately, the angular velocity detection axis and the detected axis of the gyro sensor must be matched. The detected axis to be used to know the azimuth is an axis perpendicular to the horizontal ground surface. A match between the detection axis and the detected axis increases the detection sensitivity, thereby increasing the signal-to-noise ratio to increase the detection accuracy. On the other hand, an orthogonality between the detection axis and the detected axis reduces the detection sensitivity, thereby reducing the signal-to-noise ratio to reduce the detection accuracy.
A gyro sensor mounting angle adjustment device is known that matches the detection axis and the detected axis by detecting the inclination angle of a vehicle and mechanically adjusting the mounting angle of a gyro sensor relative to the vehicle so that the mounting surface of the gyro sensor is in parallel with the horizontal ground surface (see JP-A-2001-153658, pp. 3 to 5, FIGS. 1 and 2).
Also, a navigation system is known that obtains the angular velocity around the vertical axis from the square sum average of an output of a first gyro sensor and an output of a second gyro sensor having a detection axis orthogonal to the detection axis of the first gyro sensor without having to determine the inclination angle of the road surface and those of the mounted gyro sensors. Further, a navigation system is known that computes a correction factor from an error outputted from a control circuit and a vehicle speed signal so as to correct the angular velocity around the vertical axis (see JP-A-2002-213959, pp. 8, paragraphs [0067] and [0068]).
Furthermore, a multi-axis gyro sensor is known that determines whether or not a failure has occurred therein according to outputs of a first gyro sensor and a second gyro sensor (see JP-A-2004-286529 (ABSTRACT)).
In order to mechanically adjust the mounting angle of a gyro sensor, the gyro sensor must include an adjustment component. Dedicated space is needed to substantially change the mounting angle. Therefore, the movable range of the mounting angle of the detection axis is limited. Also, if a mechanical adjustment is made such as when the angle of the detection axis is rapidly changed on an upward or downward slope, or the like, it takes a time to match the detection axis and the detected axis. This makes it difficult to increase the detection accuracy. For these reasons, as disclosed in JP-A-2002-213959, a related art technology has been proposed that obtains the angular velocity around the vertical axis from the square sum average of an output of a first gyro sensor and an output of a second gyro sensor having a detection axis orthogonal to the detection axis of the first gyro sensor without having to determine the inclination angle of a road surface and further increases the detection accuracy using a so-called correction factor. However, the inventors have found that a detection error occurs due to the first and second gyro sensors both having undergone no offset process.